Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

581
FXUS63 KLOT 250214
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
814 PM CST Sat Jan 24 2026

.KEY MESSAGES...

- Accumulating snow will result in hazardous travel conditions
  tonight into Sunday, mainly near the lake and south/east of
  I-80/I-55 corridors.

- Locally heavier snowfall rates, up to an inch per hour, are
  possible with lake enhanced snow late tonight into Sunday near
  the lake.

- Another period of very cold conditions will occur early Monday
  morning with wind chills of around 20 below zero.

&&

.MESOSCALE...
Issued at 814 PM CST Sat Jan 24 2026

Regional radar augmented by RAP mesoanalysis data depicts an
expansive region of snow extending from the central Plains and
into the Lower Great Lakes in the right entrance region of a
150kt 250mb upper-level jet streak. Based on radar reflectivity
from KLOT and AWOS/ASOS observations, the leading edge of the
snow locally extends from Amboy to DeKalb, Elgin, and Lake
Forest, Illinois. With the local forcing for ascent tied to the
aforementioned jet streak and associated frontogenesis largely
above 600mb (above the DGZ), snowflake size across our area has
remained fairly small leading to relatively muted accumulation
rates of around 0.1"/hr. Occasional higher rates near 0.5"/hr
have been observed further south near US-24 where frontogenesis
is stronger. Regardless of snowfall rate, very cold
temperatures in the single digits have led to snow-covered
roadways being very slick and hazardous, as is typical in these
sorts of regimes. The inherited Winter Weather Advisory has the
region of hazardous travel covered nicely.

With surface dew points at Rockford and Waukegan some 10
degrees lower than areas where snow is being observed, would
have to think that snow will not move any further north from
this point forward. In fact, the northern edge of the snow
shield may begin to retract southward through the overnight
hours as frontogenesis becomes refocused across central Illinois
ahead of the parent upper-level shortwave lifting northeastward
out of the Southern Plains. In all, am not expecting blockbuster
snow totals through the overnight hours and into Sunday morning
across the area, with perhaps another 0.5" or snow near the I-80
corridor to 2 to 5 inches near US-24 where snowfall duration
will be longest.

Meanwhile, a narrow band of lake effect snow being forced by
low-level convergence continues to snake west/northwestward
across southwestern Lake Michigan toward northern Cook County.
Thus far, snow has struggled to penetrate much inland, possibly
due to the effects of considerable ice cover extending several
miles offshore. With increasing low-level convergence forced by
stronger easterly flow through the night, would have to think
that the lake effect snow band should have more success moving
inland with time, even if just for a few miles. Based on the
current trajectory and west/northwestward drift of the snow
band, areas near and north of Evanston appear most in line to
see the lake effect snow overnight. After daybreak, the
expectation is for the snow band to pivot back southeastward
across northeastern Illinois during the morning hours and into
northwestern Indiana during the afternoon as the low-level wind
field backs along the backside of the departing storm system.

Forecasting snow totals from a transient lake effect snow
focused by narrow convergence zones in arctic airmasses can be
quite a challenge. At this point, felt no reason to alter the
inherited forecast calling for 1 to locally 6 inches of snow
across portions of Lake (IL), Cook, Lake (IN), and Porter
counties through the event keeping in mind the higher totals
should be confined to the closest few miles of the lakeshore
(say, east of I-90/94 if not closer to the lake). Of course, if
the band were to park over the same location for several hours,
snow totals could be locally higher. Regardless of how much snow
falls, the continued cold temperatures remaining in the single
digits overnight and only warming into the teens throughout the
day on Sunday suggest any snow that falls will be impactful.

Updated text products are in the process of being sent.

Borchardt

&&

.DISCUSSION...
Issued at 241 PM CST Sat Jan 24 2026

Through Sunday night:

Forecast on track with no meaningful changes to previous
forecast for the approaching winter storm. I am concerned that
lake effect snow could overperform a bit very late tonight into
Sunday morning over northeast IL and into northern Lake Co
Indiana Sunday afternoon, but confidence is a bit too low to
justify an upgrade to a winter storm warning at this time.

Large winter storm is slowly approaching the area this afternoon
though very dry antecedent air mass is taking some time to
saturate from top down. WSR-88D imagery does suggests that the
low level dry air is being eroded and expect areas of light
snow and flurries to begin making it to the surface soon.
Light snow will likely continue tonight, especially south of
I-80.

Most of the ascent tonight appears to be the result of upper
level divergence in the right entrance region of developing
upper level jet streak over the western Great Lakes. As such,
strongest upward vertical velocities (UVVs) are progged to be
above 600 mb, well above the very deep DGZ where weak UVVs are
progged to be neutral or even weak subsidence. This suggests
that predominant snow type for most of tonight will be smaller
flake size and resultant lower snow:liquid ratio (SLR). Nudged
the forecast SLR down some, but possibly still too high if the
snow tonight is mostly pixie dust and low SLR. Confidence wasn`t
high enough to make any big adjustments to snowfall totals, but
that is something the evening shift will need to look at for the
first half of the event tonight.

By early Sunday morning, we start to get into an area of coupled
jets with some strengthening mid-level frontogenesis. This
could result in a period of stronger UVVs below 600mb and closer
to the DGZ. This may produce heavier snowfall rates Sunday
morning where larger dendrites result in higher SLRs, at least
in mesoscale band(s). The system snow should end from west to
east from mid afternoon Sunday through early evening.

One wildcard will be the lake enhanced snow late tonight into
Sunday. While there will be a strong frontal inversion between
800-850mb through the duration of the event, limiting the depth
of the lake induced convective instability. While the depth of
the instability looks to be rather shallow, the instability
below the inversion will be quite strong with lake-850mb delta T
values around 20C. This should result in very strong ascent below
the inversion, the majority of which will be smack dab in the
middle of the DGZ. I am concerned that seeder-feeder process
from strong synoptic ascent above 600mb could result in a band
of intense lake effect snow embedded within an area of lighter
snow and flurries. Wouldn`t be surprised to see snowfall rates
>=1" per hour with the lake enhanced snow Sunday morning into NE
IL, gradually shifting into NW IN Sunday afternoon. Certainly a
play for totals solidly over 6" into northeast IL if the lake
enhancement really gets going, but confidence isn`t high enough
to justify an upgrade to a warning at this time. Will be
something that later shifts will need to closely watch.

Intensity of the lake effect should begin to decrease Sunday
evening as it loses seeder-feeder with synoptic snows shifting
east of the area. Inversion heights are progged to come up a bit
Sunday evening, so did maintain likely pops for LES across
northeast IN Sunday evening. By late Sunday evening the LES
threat should push east of Porter County, so the midnight
expiration time for the winter weather advisory looks good for
Lake/Porter Counties.

- Izzi

Monday through Saturday:

No significant changes to extended thinking at this time.

Following the weekend system, an energetic and active upper
pattern will remain in place with fast, northwesterly flow aloft
likely to guide additional disturbances across the Upper
Midwest and Great Lakes region through the week. Regarding late
Sunday night/Monday morning: latest guidance suggest we may need
some additional cold weather headlines during this period to
start the week with wind chills possibly nearing 20 below
range. Given that this is marginal/borderline advisory criteria,
we`re holding off on a wind chill advisory at this time and will
let subsequent shifts re-assess.

Latest indications point to generally precip-free conditions on
Monday as fairly robust mid-level height rises spread in from
the west through the afternoon. The nose of a ~130 kt jet streak
will impinge on the region late in the day, but at this time
only looks like it`ll drag some increasing mid and high-level
cloud cover overhead. Northwest to west-southwest breezes with a
lingering fairly tight surface pressure gradient will hold wind
chills largely below zero through the day.

On Monday night, a fast-moving and fairly robust disturbance is
slated to press southward out of the Minnesota Arrowhead Region
and across the Great Lakes. Latest guidance currently takes the
bulk of the most intense large scale forcing with this system
to our north, and will continue with a dry forecast in our area
as a result. The associated surface low will eventually drag a
reinforcing cold front through the area on Tuesday which will
send air temperatures back down to around 0 degrees Tuesday
night with colder wind chills. In the wake of the front,
forecast soundings look a bit more supportive of some
intermittent flurries as lobes of strong shear vorticity meander
southward through the afternoon and evening with increased
saturation in a thin layer at the base of a deep DGZ. Good
agreement that the boundary layer flow will remain westerly
enough to keep an follow-up LES to our east.

Another, potentially even more intense shortwave is forecast to
drop more solidly across our area on Wednesday and Wednesday
night. Guidance generally appears supportive of a period of
light snow somewhere in the vicinity, although noting a fair
amount of north- south spread in the current deterministic and
ensemble output. At this point, didn`t see any reason to stray
from the NBM-delivered chance PoPs during this period. Where
snow does fall, very cold temperatures in the single digits and
teens will once again lead to travel impacts.

Beyond this time, forecast confidence breaks down a bit, but
there`s an interesting signal of a fast-moving vort lobe backing
southwest across lower Michigan sometime during the Thursday-
Friday timeframe. This could potentially restart the LES
potential in our area, but confidence is pretty low in specifics
at this time.

Carlaw/Ratzer

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 558 PM CST Sat Jan 24 2026

Ongoing widespread light snow over northern Illinois and
northwest Indiana will continue at varying intensities through
tonight, though visibility will favor low-end MVFR to periodic
IFR levels. Confidence in exact intensity is medium as the
Chicago terminals will reside on the northern periphery of a
broad snow shield and experience some mitigating effects from
weak low-level dry air advection.

Through the night, a weakening surface high over Wisconsin will
result in light N winds, initially favoring just E of N this
evening but settling either N or just W of N due to influences
of a weak land breeze overnight.

Low-level convergence with the aforementioned land breeze and
E/NE winds over Lower Michigan will foster a dominant lake
effect snow band over western Lake Michigan overnight.
Increasing NE flow over Lake Michigan Sunday morning should push
this band inland across northeast Illinois and northwest
Indiana, gradually tracking southward along the shore. Existing
ice extending several miles offshore may limit the inland extent
of the band of snow, but ORD should be clipped and MDW likely
affected. Maintained PROB30 3/4SM visibility late morning into
early afternoon, but this window will be need to be shortened
into a potential TEMPO and be lowered to 1/2 or even 1/4SM,
particularly at MDW.

After the lake effect snow band crosses a given location Sunday
afternoon, conditions will become VFR and winds will shift NNW
with gusts over 20 knots through Sunday night.

Kluber

&&

.HYDROLOGY...
Issued at 230 PM CST Fri Jan 23 2026

River gauges, reports from local officials, and reports from
trained ice spotters continue to indicate a few ice jams across
the area due to the significant increase in river ice over
recent days. With continued cold weather into next week,
conditions will remain favorable for river ice formation. While
no widespread flooding is expected, localized ice jams may
occur.

- NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory until 6 PM CST Sunday for ILZ006-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Winter Weather Advisory until midnight CST Sunday night for
     INZ001-INZ002.

     Winter Weather Advisory until 9 PM CST /10 PM EST/ Sunday for
     INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 9 AM Sunday to 6 PM CST Monday for
     Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from noon Sunday to 6 PM CST Monday for
     Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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